Television carrier signal receiver



Aug' 12, 1941- H. A. WHEELER TELEVISIQN CARRIER SIGNAL RECEIVER OriginalFiled June '7, 1959 vw i INVENTOR R E L E E H w A D L O R A H ATTORNEYPatented Aug. 12, A1941 UNITED STATES PATENT OFFICE TELEVISION CARRIERSIGNAL RECEIVER Harold A. Wheeler, Great Neck,` N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Original applicationJune 7, 1939, Serial No.

Divided and this application September 5, 1940, Serial No. 355,442

4 Claims.

This invention relates to television carriersignal receivers, Vandparticularly to a television cants copending application Serial No.277,861,

entitled Television synchronizing system and illed June 7, 1939.

lIn accordance with present television practice, there'is developed andtransmitted a ysignal which comprises a carrier wave modulated duringsuccessive intervals or trace periods by video-frequency componentsrepresentative of light and shade values in an image being transmitted.During retrace intervals between the trace periods the carrier wave ismodulated by synchronizing pulses or components which correspond to theinitiation of successive lines and fields in the scanning of the image.At the receiver the beam is so deected as to scan and illuminate atarget in a series of parallel lines. The video-frequency components ofthe received signal are utilized to control the intensity of the beam.The line-synchronizing and held-synchronizing pulses are separated fromthe video-frequency components and are effectively separated from eachother and utilized to synchronize the operation of the receiver scanningapparatus with similar scanning apparatus utilized at the transmitter indeveloping the signal. The transmitted image is thereby reconstructed onthe target of the receiver.

In scanning of the interlaced type, the linescanning and field-scanningpulses are so related that successive fields are staggered, the lines ofone field falling between or interlacing those of a preceding eld.Because of persistence of vision, the optical effect produced is asthough each frame or group of fields comprised a multiple' of the actualnumber of lines scanned per eld and the frame-scanning frequencyequalled the fieldscanning frequency. In such systems certain of theheld-synchronizing pulses must yoccur between line-synchronizing pulses.

Furthermore, such systems conventionally .com- I l prise line-doublingpulses so that the line-synchronizingpulses are not continuous,rendering r the separation of line-synchronizing and fieldsynchronizingpulses a difficult problem. Applicants above-mentioned -copendingapplication, of which this is a divisional application, describes andclaims a television system utilizing a particular type of compositesynchronizing signal having continuous line-synchronizing pulses ofcritical amplitude and frequency characteristics and held-synchronizingpulses spaced between the line-synchronizing pulses. of the samepolarity as the line-synchronizing pulses and having predetermineddierent critical amplitude and frequency characteristics. By the use ofsuch a composite synchronizing signal, separation of theline-synchronizing and held-synchronizing pulses is greatly facilitated.

Also, in television systems it is desirable to.,

control automatically various receiver-operating erage intensity of thecarrier wave independent of lintensity variations due tolight-modulation components. For this purpose, in systems wherenegatively-modulated carrier waves are utilized, that is, where adecrease in carrier-wave amplitude corresponds to an increaseinillumination, the synchronizing pulses generally appear as outwardmodulation peaks and the peak value of the synchronizing pulses providesa convenient measure of the carrier intensity variations independent ofthe light-modulation components. For various reasons, however, includingthe fact that the synchronizing signals utilized in the prior art haveincluded field-synchronizing pulses of either the same or greateramplitude than the line-synchronizing pulses and the fact that thesesynchronizing pulses are not uniformly spaced with respect to the linepulses in interlaced systems, the irregular spacing of these pulsestends to ail'ect the control effect derived from the signal and ameasure of the intensity variations in question has been difficult orimpossible to obtain without too great a time constant in the circuit.

It is an object of the present invention, therefore, to provide atelevision receiver including an improved automatic amplificationcontrol which avoids one or more of the above-mentioned disadvantages ofprior art arrangements.

It'is still another object of the invention to l amplication controlarrangement which is respons'ive only to the line-synchronizing pulsesof a composite signal including both line-synchronizing andfield-synchronizing pulses.v

i In accordance with the invention, a television carrier-signal receiveradapted to receive a carrier. wave modulated with video-frequency,components and acomposite synchronizing signal includingfield-synchronizing components and line-synchronizing components ofgreater amplitude than said eld-synchronizrlng components comprisesmeans for reetifylng only the linethe frequency of theline-synchronizing com-' ponents, and means are coupled to thetimeconstant circuit for deriving a control effect therefrom and forutilizing it to control an operating characteristic of the receiver, forexample. the gain of an amplifying stage of the receiver.

In the accompanying drawing, Fig. l is a circuit diagram, partlyschematic, of a complete television receiving system embodying theinvention, while Fig. 2 comprises a graph utilized to illustrate certainof the operating characteristics of the receiver of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, there is showna circuit diagram, partly schematic, of a complete television receivingsystem of the superheterdyne type'including, in cascade', an antennasystem 30, 3l, a radio-frequency amplifier 32, an oscillatormodulator33, an intermediate-frequency amplifler 34, a detector 35, avideo-frequency amplifier 36, and an image-reproducing device 31, suchas a cathode-ray signal-reproducing tube.

A synchronizing-signal separator *38 also is coupled to the outputcircuit of the detector 35 and its output circuit is, in turn, coupledto linefrequency and field-frequency wave generators 39 and 40 by way ofinter-synchronizing-signal separating apparatus, indicated generally at4I. The generators 39 and 44|) have their output cirpulses are appliedto thel generators 39 and 46 to synchronize their operations with thecorresponding apparatus at the transmitter. .The apparatus 4I maybe ofconventional design or may be in accordance with that described andclaimed in applicants above-mentioned copending application. Theintensity of the beam of the reproducing device 31, is thus modulated orcontrolled in accordance with the video-frequency voltages impressedupon its control electrode'in the usual manner. Scanning waves developedby the generators 39 and 40, controlled by the synchronizing4`components, supplied from the apparatus 4I, are utilized in theconventional mancuits connected to the scanning elements of the device31 in conventional manner. .Theparts of the system representedschematically may be of any conventional type or operation.

Since the system of Fig. 1 as thus far described is, in general, wellknown in the art, a

`detailed description of the system and its operation is deemed to beunnecessary. Briefly, however, a television-modulated carrier wave isintercepted by the antenna system 30,' 3| and selectively amplified inthe radio-frequency amplier 32, from which it is impressed upon theoscillator-modulator 33 wherein it is converted into anintermediate-frequency signal which is thereupon further selectivelyamplified in the intermediate-frequency amplifier 34. The amplifiedintermediate-frequency signal is thus delivered from amplifier 34 todetector 35 in which there is developed the composite modulation signalcomprising the video-frequency components and This' ner to deflect thescanning beam of the imagereproducing device 31, for example, byproducing electric flelds of saw-tooth wave form which deflect theelectron beam of the signal-reproducing tube in two directions normal toeachfother so as to trace the usual rectilinear scanning pattern uponthe target of the reproducing device, thereby to reconstruct thetransmitted image.

Referring now more particularly to the portion of the system of Fig. 1constituting the present invention, there is provided an amplificationcontrol circuit 42 which may comprise a conven- -tional diode rectifier59 connected across a transformer secondary winding 6l! by way of a loadcircuit including a parallel-connected `resistor 6I and by-passcondenser62, the time constant of which is considerably greater than theperiod of the line-synchronizing pulses but usually less than that ofthe iield-synchronizing pulses. The winding 60 is coupled to atransformer primary winding 63 which is connected to the output circuitof the intermediate-frequency amplier 34, while the negative terminal ofthe load resistor 6I is coupled, by way of a suitable filter includingseries resistors 64 and shunt condensers 65, to the control electrode ofone or more of the signal-translating tubes in the stages 32, 33 and 34.

In Fig. 2 there is illustrated the envelope of one-half of the signalwhich is received by theV receiver of Fig. 1. In considering theoperation of the-amplification control circuit 42, it will be seen thatan improved result is obtained by virtue of a modication of design andthevv novel wave form of the signal which is applied thereto from theintermediate-frequency amplifier v 34. This signal includes a compositesynchronizing signal including field-synchronizing components andcontinuous line-synchronizing pulses L, L of greater amplitude than thefield-synchronizing pulses F. The line-synchronizing pulses, havepredetermined critical amplitude and frequency characteristics and thefield-synchronizing pulses F are spaced between the line-synchronizingpulses, are of the same polarity as the linesynchronizing pulses and'have predetermined different critical amplitude and frequencycharacteristics, Vspecically a lower frequency and a lesser amplitude.The circuit 42 including the diode rectifier 53 thus peak-rectifies theapplied signal to derive across its load impedance 6I, 62 aunidirectional negative bias voltage which increases in proportion totheamplitude of the received carrier wave and independent of itslightmodulation components. It will be appreciated that, since thefield-synchronizing pulses of the. novel composite signal are of aconsiderably lesser amplitude than the line-synchronizing pulses andsince the time constant of the rectifier load circuit 6I, 62 issubstantially greater than the period of the line-synchronizing pulses,

. 2,252,148 theiield-synchronizing pulsesdo not undesirably .l bias`voltage for automatically controlling vari-` aiect thev operation ofthe rectifier circuit as they do in the case ofsimilar systems of theprior art, as explained above. That is, only the peaks of theline-synchronizing pulses are rectified and these peaks provide aprecise measure of the intensity variations of the signal-carrier wave.The unidirectional control bias voltage thus developed across the loadcircuit 6 I 62 is illustrated by curve G1-in-Flg. 2. Such a voltage isreadily smoothed out bythe filter elements 65, 64 of the A'. V. C.system, thereby providing a steady unidirectional control-bias voltageof the exact required amplitude. This voltage, being applied negativelyto the control electrodes of one or more tubes in the stages 32', 33 and34, serves to vary the 4 amplication in these stages inversely inaccordance with the variations in received carrier intensity andindependent of variations corresponding to light-modulation components,so as to provide a signal input to the detector 35 having relativelysmall variations in amplitude over a wide range of receivedsignal-carrier wave variations, according to conventional A. V. C.practice.

In such control systems of the prior art where the field-synchronizingpulses affect the control, it was necessary that the time constant ofthe control circuit have a value much higher than the period of thefield-synchronizing pulses. In the system of thepresent invention,however, the control is independent of the field-synchronizing pulsesand the time constant of the control rectifier and illter circuits 6|,62, 64, 65 may be made much smaller Without irregularity of control;specifically, the time-constant circuit may have a time constantsuiiiciently long only to suppress components of frequencies of theorder of the frequency of the line-synchronizing components. Thissmaller time constant is advantageous in that it minimizes the durationof theeiect of strong transient disturbances, such as static. 'I'hegreatest benefit in minimizing the effect of such disturbances isobtained if the 'time constant of the control circuit is of a valuesomewhat less than that of the iield period, although its value is stillmuch greater than the line period. 'Ihe single requirement of the systemof the present invention is that the time constant of the controlcircuit have a value much greater than the line period ofthe system. Itmay be of the same order of magnitude or even less than the fieldperiod, although such rapid control is ordinarily not necessary. Ingeneral, it will be satisfactory if it is somewhat greater than thefield periodbut yet not nearly great enough to smooth out disturbancessuch as caused by field pulses in systems of the prior art. Therefore,when this novel composite synchronizing signal is used with anegatively-modulated carrier wave such as described in the instant case,a control bias voltage may be readily developed in accordance withvariations in peak value of the linesynchronizing pulses alone foreffecting a precise automatic control of some characteristic of thesystem, such as automatic amplification control, in accordance withvariations in the received carrier wave intensity and independent oflightmodulation components.

It will be readily apparent that various other improved automaticcontrols, such as automaticous characteristics of the system may beobtained in a manner analogous to that described above bypeak-rectifying the modulation signal developed by detector 35. In thiscase, as in the arrangement illustrated, a quick and highly accuratecontrol is obtained by reason of the fact that the peaksoftheline-synchronizing pulses are available for rectification withoutVinterference from the field-synchronizing pulses.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled `in the art that various changes and modifications may be madetherein without departing from the y invention, and it is, therefore,aimed in the appended claims to cover all such 'changes andVmodifications as fall within the true spirit and scope of theinvention. VWhat is claimed is:

1. A television carrier-signal receiver adapted to receive a carrierWave modulated with videofrequency components and a compositesynchronizing signal including held-synchronizing components andline-synchronizing components of greater amplitude than saidfield-synchronizing components comprising, means for rectifying only theline-synchronizing components of the received signal, saidline-synchronizing components having an amplitude varying only inaccordance with the amplitude of the received signal, a time-constantcircuit coupled to said rectifying means and having a time constantsufilciently long only to suppress components of frequencies of theorder of the frequency of said line-synchronizing components, and meansfor deriving a control effect from said time-constant circuit and forutilizing it to control an operating characteristic of said receiver.

2. A television carrier-signal receiver adapted to receive a carrierWave modulated with videofrequency components and a compositesynchronizing signal including field-synchronizing components andline-synchronizing components ofv greater amplitude than saidfield-synchronizing components comprising, means for amplifying thereceived signal, means for rectifying only the line-synchronizingcomponents of the received signal, said line-synchronizing componentshaving an amplitude varying only in accordance with the amplitude of thereceived signal, a time-constant circuit coupled to said rectifyingmeans and having a time constant sufficiently long only to suppresscomponents of frequencies of the order of the frequency of saidline-synchronizing components, and means for deriving a control meansfor amplifying the received signal, means for peak-rectifying only theline-synchronizing components of the received signal, saidline-synchronizing components which are rectified having an amplitudevarying only in accordance with the amplitude of the received signal, atimeconstant circuit coupled to said rectifying means and having a timeconstant sumciently long only to suppress components offrequencies-'ofthe order of the frequency of said line-synchronizing components, andmeans for deriving a control eect from said time-constant circuit andfor utilizing it to vary the gain of said amplifying means inversely inaccordance with the amplitude of the received signal.`

4. A television carrier-signal receiver adapted to receive a televisionsignal including .videofrequency` components and held-synchronizingnents comprising, means for amplifying the re 15 ceivedsignaL means forrectifying only line-synchronizing components of the received signal,said line-synchronizing 'components which are rectied having anamplitude varying only in accordance with the amplitude of the receivedsignal, a time-constant circuit coupled to said rectifier and having atime constant suilciently long only to suppress components ofyfrequencies of the order of the frequency of said line-synchronizingcomponents, and means, for deriving a control eiect from saidtime-constant circuit and i'or utilizing it to vary the gain of saidamplifying means inversely in accordance with the amplitude of thereceived signal.

HAROLD A. WHEELER.

